Process for beneficiating and cleaning biomass

ABSTRACT

A process for cleaning and beneficiating biomass is described which may allow removal of entrained salts and light volatiles from biomass materials. The process may also minimize energy use through capturing steam and flue gases for re-use. The process may generally comprise the following steps: prewashing and/or preheating a biomass, pressurizing the biomass in a steam explosion vessel, rapidly depressurizing the steam explosion vessel, releasing the steam from the steam explosion vessel entrained with fine lignin-enriched particles into a cyclone-type gas expansion vessel, routing the steam from the gas expansion vessel to the input hopper, subjecting the biomass to a second washing step, mechanically removing a portion of the water from the biomass, and evaporatively heating the biomass.

PRIORITY CLAIM

This application is a divisional of and claims priority to U.S.non-provisional application Ser. No. 15/877,937 filed Jan. 23, 2018,which claims priority to U.S. provisional application No. 62/508,043,filed May 18, 2017. Application Ser. No. 15/877,937 and application No.62/508,043 are each incorporated herein by reference in theirentireties.

TECHNICAL FIELD

This disclosure relates generally to the field of physical and chemicalprocesses for converting biomass into an end product suitable for use asfeedstock for solid fuel energy production. More particularly, thedisclosure relates to processes for converting biomass which may bebuilt with a modular design and modified to fit particular fieldrequirements.

BACKGROUND

Biomass encompasses a wide array of organic materials including wood,woody waste, agricultural residues, and crops grown specifically forenergy production. The U.S. alone generates billions of tons of biomassannually. Beneficiated biomass, in which the moisture content has beenreduced and the energy density has been increased, can be used as afeedstock for several products, including pellets for residentialheaters, hydrocarbon liquid fuels, cellulosic ethanol, solid fuel tosupplant coal, or for production of synthetic natural gas.

Beneficiation is the treatment of raw material to improve physical orchemical properties and typically includes steps to increase the energydensity. Conventional methods to beneficiate biomass include heat/steamtreatment, torrefication, and pressure extrusion (“densification”).These methods have not been designed necessarily to remove entrainedsalts and thus do not produce acceptable fuels from many biomass inputsbecause remaining salts can lead to fouling, slagging, or corrosion whencombusted. Consequently, only clean materials such as heartwood can beused as a feedstock, leaving the less expensive “hogged” biomassmaterial as waste. Heat/steam treatment and pressure extrusion methodsare also not designed to remove light volatiles from the feedstock,rendering the product potentially unusable as a solid fuel to supplantcoal because of premature ignition in the pulverizer or burner.Moreover, these methods are energy intensive, leading to an unfavorableoverall energy balance, and thus economically limiting the use ofbiomass for its intended applications.

Another benefit of beneficiation of raw materials for fuel sources isthat it provides a fuel source with a low carbon footprint. The carbonfootprint is small due to the way carbon is scored for CO₂ greenhousegas production. Carbon from renewables like wood and wood byproducts arenot as significant in contributing to atmospheric CO₂ concentrations ascarbon from fossil sources like coal because the carbon comes from CO₂which was in the atmosphere to begin with, instead of adding carbon frompreviously inaccessible sources in the ground.

As an alternative, a re-designed heat/steam treatment of biomassmaterials with additional cleaning steps can substantially improve thequality of densified biomass while also reducing the amount of requiredenergy. Heat/steam treatment has a variety of descriptions and methodsin the literature and centers on biomass drying and energydensification. Most heat/steam systems dry the material early in theprocess, even before the heat/steam process.

Thus, there is a need for beneficiation methods to further removeentrained salts and light volatiles from biomass materials. It may alsobe desirable to increase the friability of the material, and minimizeenergy use through capturing steam and flue gases for re-use.

SUMMARY

The chemical and steam-explosion processes described herein produces asolid biomass-based fuel for use either by itself or blended withanother fuel source. According to one aspect of the present disclosure,heat and steam-explosion beneficiation of biomass is described which mayproduce a renewable solid fuel that has a high energy density (around8500 to around 10500 BTU/pound, comparable to a sub-bituminous coal),low contaminant (with respect to sulfur and slagging-, fouling-, andcorrosion-inducing elements Na, K, and Cl), and a relatively smallcarbon footprint.

According to another aspect of the present disclosure, the processesdescribed herein may allow otherwise waste biomass, such asnon-heartwood scraps or salt-laden wood, to be used for fuel rather thanrot in compost piles, thereby preventing release of the potentgreenhouse gas methane into the atmosphere.

According to another aspect of the present disclosure, thelignin-enriched content removed from the gas expansion vessel describedherein may provide a source for chemical feedstock, sticky binders,non-petrochemical-based polymer replacements, or ultra-high energydensity fuel if it is not blended back into the beneficiated biomassremoved from the main steam explosion vessel.

According to another aspect, a process is described comprising one ormore of the following steps: prewashing and/or preheating a biomass;pressurizing the biomass in a steam explosion vessel or reaction vessel;rapidly depressurizing the reaction vessel; releasing the steam from thereaction vessel entrained with fine, lignin-enriched particles into acyclone-type gas expansion vessel; routing the steam from the gasexpansion vessel to an input hopper; subjecting the biomass to a secondwashing step; mechanically removing a portion of the water from thebiomass; and evaporatively heating the biomass.

According to another aspect, the steam explosion vessel or reactionvessel comprises an inner perforated screen separating the biomass fromthe main body of the steam explosion vessel and with one or moreperforated screen fingers disposed within the steam explosion vessel andpositioned within the biomass to increase exposure of the biomass tosteam.

According to still another aspect, the steam explosion vessel may have avertical orientation. In some configurations, the steam explosion vesselmay be provided with o-ports, gate valves, and/or autoclaves to seal thetop and bottom of the steam explosion vessel. The steam explosion vesselmay include a perforated screen liner with one or more screenin/down-comers. The steam explosion vessel may also be provided with arapidly opening valve such as a fast-opening offset butterfly valve.

According to another aspect, the step of rapidly depressurizing thesteam explosion vessel disrupts the biomass structure and releasesbiomass salts and light volatile organic compounds entrained within thebiomass and produces steam containing at least partially lignin-enrichedfine particles. The cyclone-type gas expansion and gas-release vesselmay be configured to capture the entrained fine lignin-enrichedparticles.

According to still another aspect, various steps are described to reducethe energy required to complete the process. For example, the step ofrouting the steam from the gas expansion vessel to the input hopper mayrecapture heat from the captured steam and steam condensate to heat andwet the biomass in the input hopper. Insulation of the steam explosionvessel and other components may save energy, as well as routing of steamand use of heat from flue gas to improve energy balance of plant.

According to yet another aspect, the disrupted biomass may be subjectedto a second washing step to remove additional salts and light volatileorganic compounds derived from the disrupted biomass. This secondwashing step may be done in a separate wash tank or washing apparatus.In some configurations, the entrained fine lignin-enriched particlescaptured in the gas expansion vessel may be added to the biomass in thesecond washing step. In other configurations, they may be added at alater step or not added and used for a separate purpose.

According to another aspect, mechanically removing a portion of waterfrom the biomass may be accomplished with extrusion water removal steps,wherein the resulting biomass comprises less than about 50% water byweight and wherein additional salts and light organic compounds derivedfrom the disrupted biomass are removed with the water.

In some configurations, mechanically removing a portion of water fromthe biomass may be accomplished through use of one or more of a screwpress, roller press, torque/grinder presses, etc.

According to another aspect, the biomass may be evaporatively heated toremove an additional portion of the water and produce a friable biomass,wherein the resulting friable biomass comprises less than about 25%water by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments and aspects of the present disclosure are shown anddescribed in reference to the numbered drawings wherein:

FIG. 1 shows a flow diagram of chemical and physical steps and featuresinvolved in the beneficiation/wash process described in the presentdisclosure;

FIG. 2 shows a schematic of system components used in thebeneficiation/wash process;

FIG. 3 shows a perspective view of an exemplary steam explosion vesselor reaction vessel;

FIG. 4 shows a side view of the reaction vessel of FIG. 3 ;

FIG. 5 shows a cross-sectional view of the reaction vessel of FIGS. 3and 4 , taken along line 5-5 of FIG. 4 ;

FIG. 6 shows a perspective view of an exemplary gas expansion vessel;

FIG. 7 shows a side view of the gas expansion vessel of FIG. 6 ;

FIG. 8 shows a cross-section view of the expansion vessel of FIGS. 6 and7 , taken along line 8-8 of FIG. 7 ;

FIG. 9 shows a front, perspective view of an exemplary configuration ofa dewatering module;

FIG. 10 shows a rear, perspective view of the dewatering module of FIG.9 ; and

FIG. 11 shows a perspective view of an exemplary evaporative dryer.

It will be appreciated that the drawings are illustrative and notlimiting of the scope of the invention which is defined by the appendedclaims. The embodiments shown accomplish various aspects and objects ofthe invention. It will be appreciated that it is not possible to clearlyshow each element and aspect of the present disclosure in a singlefigure, and as such, multiple figures are presented to separatelyillustrate the various details of different aspects of the invention ingreater clarity. Similarly, not all configurations or embodimentsdescribed herein or covered by the appended claims will include all ofthe aspects of the present disclosure as discussed above.

DETAILED DESCRIPTION

Various aspects of the invention and accompanying drawings will now bediscussed in reference to the numerals provided therein so as to enableone skilled in the art to practice the present invention. The skilledartisan will understand, however, that the methods described below canbe practiced without employing these specific details, or that they canbe used for purposes other than those described herein. Indeed, they canbe modified and can be used in conjunction with products and techniquesknown to those of skill in the art in light of the present disclosure.The drawings and the descriptions thereof are intended to be exemplaryof various aspects of the invention and are not intended to narrow thescope of the appended claims. Furthermore, it will be appreciated thatthe drawings may show aspects of the invention in isolation and theelements in one figure may be used in conjunction with elements shown inother figures.

Reference in the specification to “one embodiment,” “one configuration,”“an embodiment,” or “a configuration” means that a particular feature,structure, or characteristic described in connection with the embodimentmay be included in at least one embodiment, etc. The appearances of thephrase “in one embodiment” in various places may not necessarily limitthe inclusion of a particular element of the invention to a singleembodiment, rather the element may be included in other or allembodiments discussed herein.

Furthermore, the described features, structures, or characteristics ofembodiments of the present disclosure may be combined in any suitablemanner in one or more embodiments. In the following description,numerous specific details may be provided, such as examples of productsor manufacturing techniques that may be used to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that embodiments discussed in thedisclosure may be practiced without one or more of the specific details,or with other methods, components, materials, and so forth. In otherinstances, well-known structures, materials, or operations may not beshown or described in detail to avoid obscuring aspects of theinvention.

Before the present invention is disclosed and described in detail, itshould be understood that the present invention is not limited to anyparticular structures, process steps, or materials discussed ordisclosed herein, but is extended to include equivalents thereof aswould be recognized by those of ordinary skill in the relevant art. Morespecifically, the invention is defined by the terms set forth in theclaims. It should also be understood that terminology contained hereinis used for the purpose of describing particular aspects of theinvention only and is not intended to limit the invention to the aspectsor embodiments shown unless expressly indicated as such. Likewise, thediscussion of any particular aspect of the invention is not to beunderstood as a requirement that such aspect is required to be presentapart from an express inclusion of that aspect in the claims.

It should also be noted that, as used in this specification and theappended claims, singular forms such as “a,” “an,” and “the” may includethe plural unless the context clearly dictates otherwise. Thus, forexample, reference to “an evaporative dryer” may include an embodimenthaving one or more of such dryers, and reference to “the vibratoryscreen separator” may include reference to one or more of such vibratoryscreen separators.

As used herein, the term “generally” refers to something that hascharacteristics of a quality without being exactly that quality. Forexample, a structure said to be generally vertical would be at least asvertical as horizontal, i.e. would extend 45 degrees or greater fromhorizontal. Likewise, something said to be generally circular may berounded like an oval but need not have a consistent diameter in everydirection.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint while still accomplishingthe function associated with the range.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember.

Concentrations, amounts, proportions and other numerical data may beexpressed or presented herein in a range format. It is to be understoodthat such a range format is used merely for convenience and brevity andthus should be interpreted flexibly to include not only the numericalvalues explicitly recited as the limits of the range, but also toinclude all the individual numerical values or sub-ranges encompassedwithin that range as if each numerical value and sub-range is explicitlyrecited. As an illustration, a numerical range of “about 1 to about 5”should be interpreted to include not only the explicitly recited valuesof about 1 to about 5, but also include individual values and sub-rangeswithin the indicated range. Thus, included in this numerical range areindividual values such as 2, 3, and 4 and sub-ranges such as from 1-3,from 2-4, and from 3-5, etc., as well as 1, 2, 3, 4, and 5,individually. This same principle applies to ranges reciting only onenumerical value as a minimum or a maximum. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

Turning now to FIG. 1 , diagram of the chemical and physical processesthat underlie this teaching are shown. The process described hereindisrupts the cross-linking barriers in biomass fibers to defeat freshbiomass recalcitrance to produce a dry, friable, high-energy-densitymaterial with reduced amounts of salts and light volatile material.Final drying may also increase the friability of the material.Friability implies that it can be ground to a powder with a sizedistribution comparable to that of coal when ground for use in apulverized coal power plant. Friability is desirable so the beneficiatedbiomass can be used in a pulverized coal power plant, by itself or mixedwith coal, without major capital modifications. All of these effectsallow use of lower cost input material that can include whole biomassinput rather than expensive heartwood or clean material. With thecombined benefits produced through this teaching, biomass inputs mayinclude slash, salt-laden hogged woodpiles, and waste piles, any ofwhich can be used as fuel for boilers without pre-ignition, slagging,fouling, or corrosion.

Biomass consists primarily of cellulose, hemicellulose, and ligninlocated in the secondary cell wall of relevant plant materials.Pretreating and in-process treating of the wet biomass with pressurizedsteam produces several chemical reactions, explicitly described here.Wet oxidation is initiated, which starts the degradation of the ligninas well as produces some acid in the slurry as small side groups arecleaved from the hemicellulose to form small organic acids (for example,small side groups ranging from small acetyl groups to acetic acid). Acidis also produced in the oxygen-promoted depolymerization of celluloseand hemicellulose chains. Subsequent acid hydrolysis from the producedacid breaks ester bonds and continues polymer decomposition. No acidneed be added externally to the process: the acid may be produced insitu and used for subsequent breakdown of polymers, especially the esterlinkages between lignin polymers and lignin-cellulose polymericcross-linkages.

Throughout this process, hydrogen bond disruption occurs through whichhydrogen bonds interconnecting polymer fibers of cellulose andhemicellulose are also broken due to increased vibrational energy andthe lowering of the dielectric constant in hot water. Once the fiberwalls have been weakened after a certain residence time in the steamexplosion vessel or reaction vessel, the pressure is rapidly released.With the rapid release of external pressure, the internal pressurewithin the cell must also be released, resulting in the bursting of theweakened cell wall. The steam explosion step breaks open the fibers toexpose salts and light volatiles formed primarily from degradation ofthe hemicellulose for subsequent dissolution and extrusion. During steamexplosion, the lignin also is affected. The ether linkages of highmolecular weight lignin break to generate lower molecular weight lignin.Furthermore, it melts, redistributes, condenses, and forms beads on thesurface of the cellulose micro-fibrils and thus increases the porosityof the microfibers.

FIG. 2 shows a schematic of the equipment to process the biomassaccording to the steps described herein. The process may initiallyemploy a macerating operation (210) to appropriately size and exposesurface area from, for example, woody wastes or other dense materials.Generally, macerated materials enter the process at input hopper 220 inpieces of about one-half to quarter inch and smaller size. Themacerating steps may macerate the biomass into various sizes dependingon the desired results, for example, the biomass may be macerated intopieces of about 3.81 centimeters (1.5 inches) to about 0.635 centimeters(0.25 inches). Conveyor belts may take the macerated biomass from theinput hopper to the pre-wash processing unit 230.

The macerated biomass input is introduced to a pre-wash processing unitor container 230. Besides wetting the material for subsequent steamexplosion, this step can be used to remove unwanted external ash, dirt,and initiate a start at removing the salts. A short sluice between theinput hopper and pre-wash unit removes the heavy rocks, pebbles, sand,etc. while allowing the lighter, floating biomass to be flowed into thepre-wash unit. The rocks, sand, etc. sink to the bottom trap, which canbe opened periodically to remove them. A magnetic trap may be added(either at the macerator/hopper 220, the pre-wash container/processingunit 230, or at another point in the cycle) for removing any remainingiron scrap from the harvesting process such as bolts or nails.

Beginning at the input hopper 220 and/or the pre-wash unit 230 andextending through the drying steps, insulation of the external surfacesof the parts of the system may improve energy balance. Preservation ofheat from one batch of biomass to the next may build a steady statetemperature approaching water's boiling point and recycle what otherwisewould have been lost energy. As described below, steam from thesteam-explosion step may be directed to the input hopper 220, addingheat and starting the chemical processes that weaken the cell walls.Re-use of steam rather than just direct release to the environmentconserves heat and improves the energy balance.

The pre-wash unit 230 may be an agitated/stirred vat or a dynamictrommel system, wherein water is contacted to the biomass conveyed viaan auger up to the holding tank for the steam explosion vessel, orreactor, 240. The trommel may comprise, for example, an inclinedscrew/auger surrounded by a screen in a partially-filled water tank. Thebiomass may be wetted as it moves upward along the screw/auger whiledirt is mechanically separated and falls through the screen to a removalcontainer. The auger/water slurry may be surrounded by a screen throughwhich the water and entrained dirt and salt can exit. In the trommelarrangement, an auger may be welded into a screen (for example, a screenwith one-quarter inch holes) through which the water, dissolved salts,and any remaining entrained dirt can exit with the dirt falling to thebottom of the tank. The auger/screen unit may be semi-submerged in thewater bath and inclined at about a 10 degree angle. The motion of theauger moves the in-coming biomass up through the trommel. Paddles placedperiodically along the auger help move the biomass into and out of thewater bath as it moves up and through the prewash unit, therebyagitating and washing the biomass. Nozzles above the trommel spray wateron the biomass and clean it further. The biomass emerges from the augerand falls into a holding tank for the reactor. To remove contaminatedwater from the tank, a fraction may be pumped out to the water treatmentplant, and replaced with an equal amount of fresh water.

At the pre-wash unit 230, chemicals suitable for permeating anddisrupting biomass fibers and promoting wet oxidation and/or acidhydrolysis to disrupt hemicellulose and lignin cross-linking, andsolubilize other contaminants, may also be added. The input biomassmaterial could be mixed with appropriate chemicals to permeate the plantfibers and accelerate the chemical processes, including hydrogen-bondbreaking, wet oxidation, and acid hydrolysis reactions to disrupt thehemicellulose and lignin cross-linking barriers. Additional chemicalapplications, depending on the physical properties of the biomass input,may comprise aqueous solutions of methanol, ammonium carbonate orcarbonic acid. Other potential chemical applications include ammonia(leads to AFEX (Ammonia Fiber Explosion) process), acetone,acetonitrile, and different combinations of them. In addition, the useof solvents such as methanol may be desirable for biomass input havingpreservatives or a soft wood content to dissolve creosote or resinscontained in the woody biomass to allow the beneficiation chemicalsbetter contact with the fibers. For example, a 50:50 water:methanol mixby volume is effective at dissolving glue components (e.g. formaldehyde)used in plywood/demolition wood. Because of the higher volatility ofmethanol, the reactor must be designed for higher pressures to achievethe same temperature and effectiveness as pure water. For example,pressures to 650 psi may be required and must be pre-engineered inspecially made systems for these higher pressures for safety.

After the pre-wash unit 230, the biomass is mechanically passed into avertically oriented steam explosion vessel or reaction vessel 240 forchemical conditioning on the cell walls followed by steam-explosion.FIG. 3 shows a perspective view of the reaction vessel 240, FIG. 4 showsa side view, and FIG. 5 shows a cross-sectional view of the reactionvessel taken along line 5-5 of FIG. 4 . A valve 238 may allow forselectively opening and closing of the passageway from the pre-washprocessing unit 230 to the steam explosion vessel 240. A steam input 251may be disposed on the reaction vessel 240, connecting the reactionvessel to a boiler 250 or other source of steam (e.g., steamgenerator/thermal fluid heater combination). The vertical arrangement orgenerally vertical arrangement, with the input gate/valve 238 at top andoutput gate (such as an autoclave door) 241 on the bottom, may providebenefits over a horizontal orientation, including: ease of loading withmechanical or pneumatic conveyors; taking advantage of gravity forloading and unloading; size of biomass chips less critical compared tohorizontal loading with potentially less grinding required at front end;and footprint of plant reduced. A horizontal-oriented reaction vesselmodule may also be used, but in some applications may be less effective.

All the surfaces exposed to the reaction in the reaction vessel 240 andsubsequent wet biomass in the process may be formed from stainlesssteel. While other materials may be possible, in the presentconfigurations no treatments or coatings that would allow for the use ofless expensive carbon steel were found to be effective in the hot, wetreaction conditions with rapid expansion/contraction phasescorresponding to high and low pressure conditions in the reactionvessel. The doors on either end of the reaction vessel 240 may becomprised of autoclave doors, o-port valves, knife valves, etc.

The reaction vessel 240 may comprise an inner perforated screen 243. Theperforated plate/screen 243 may be formed from any suitable material,for example, stainless steel, and may be suspended within the reactionvessel with sufficient space between the screen 243 and reaction vesselwall, allowing the steam direct access to a much greater cross sectionof biomass. For example, the screen may separate the biomass from thewall of the reaction vessel by about 1.27 centimeters (0.5 inch) toabout 5.08 centimeters (2 inches). In this manner, the perforated screen243 may separate the biomass from the main body of the reaction vessel240. The size of the holes in the screen 243 can be chosen based on thesize of the biomass chips about may typically be about 0.3175centimeters (one-eighth inch) to about 0.635 centimeters (one-quarterinch). The range could be expanded for smaller materials, such assawdust and larger materials such as empty fruit bunches.

The screen 243 may also be provided with one or more perforated screenfingers 320 (see FIG. 5 ) disposed within the reaction vessel 240 andpositioned within the biomass to increase exposure of the biomass tosteam. The perforated screen fingers 320 may be positioned away from thewall of the reaction vessel 240 to maximize exposure of the biomass tothe steam. Perforated screen fingers may be downcomers (open to steamfrom the top of the reaction vessel) and/or upcomers (open to steam fromthe bottom of the reaction vessel, as in the upcomer 320 shown in FIG. 5). For example, perforated screen downcomers (stalactite configuration)or upcomer(s) (stalagmite configuration) may be suspended/extended fromthe top/bottom. The pattern and number of fingers may be configured suchthat the maximum distance of any biomass to steam headspace is around 9inches to increase steam penetration.

The use of the perforated screen 243 and/or screen finger(s) 320 mayallow steam to surround the biomass, and may allow a large volume ofbiomass that would otherwise insulate from the steam, to be exposed tothe steam, resulting in more fiber disruption. Without a perforatedscreen 243, a large volume of biomass may otherwise insulate thematerial from the steam, resulting in significantly less fiberdisruption. The addition of fingers to shorten the maximum distancebetween a steam channel and the most deeply buried biomass may allowboth better steam entrance/exposure to biomass material andbetter/quicker steam exit and hence better steam-explosion. Theseplurality of perforated finger screen liners may have a plurality ofscreen hole sizes.

After closing the reaction vessel 240, pressurized saturated steam isintroduced into the reaction vessel from a boiler or steam generator250. The exact reaction conditions (pressure, temperature, residencetime) depend on the nature of the biomass input. Specific examples aregiven below in Table I. Typical conditions for woody biomass might be400 to 450 psi, 448° F. for 15 to 20 minutes. Herbaceous materials mayrequire less severe conditions (350 to 420 psi for 15 to 20 minutes).The temperature of the saturated steam is directly related to thepressure through the well-known Steam Tables.

Chemical effects such as hydrogen bond breaking, wet oxidation, and acidhydrolysis of the cellulose, hemicellulose, and lignin, occur during theretention time, weakening the cell wall in preparation for the rapiddepressurization.

The profile of the applied chemical treatments may be tailored forparticular biomass inputs. The reaction vessel's temperature, pressure,biomass residence time, and chemical concentrations are carefullycontrolled so as to optimize process conditions for a particular biomassinput. Table I lists varying conditions for exemplary biomass inputs.(Table I is given by way of example, not of limitation. Other types ofbiomass inputs not typically used, such as railway ties, may requiredifferent conditions, such as different solvents like methanol, 50:50methanol:water, pressures beyond 600 psi in the reaction vessel, and/orextra time in the reaction vessel.) Sensors may be strategicallypositioned within the reaction vessel 240 to provide real-time feedbackto the control system to ensure optimization. The details of the appliedchemical treatments versus particular biomass inputs and conditions maybe captured in a library of algorithms and programmed to be applied.

After a predetermined residence time dictated by the characteristicbiomass input, the pressure is released rapidly in the reaction vessel240, for example by rapidly opening a valve 242. The rapid pressurerelease may produce a stream of outrushing steam. The perforated screen243, which had allowed a better ingress of the steam to the biomass, nowmay give a larger cross section for rapid release and egress. Thediameter of the rapidly opening pressure release valve 242 is the ratedetermining step for pressure release, not resistance from steam tryingto find its way through the biomass. Larger valves allow for quickerdepressurization, and different types of pressure release valves allowfor different outcomes. Because of the large pressures (force per squareinch) and surface areas involved, many types of valves, such as ballvalves, may produce huge frictional forces that oppose fast opening. Toavoid this problem, an offset butterfly valve may be used, in which anopening counter-force from the smaller side of the butterfly partiallyoffsets the closing force on the other side of the valve. Thisforce-balancing makes opening the valve in less than 500 microsecondspractical with an off-the-shelf offset butterfly valve with a steppingmotor. The minimized torque may allow for controlled but still fastopening. Alternatively, in another configuration, several smaller valvescould be ganged together to open simultaneously. The combined crosssection of the smaller valves may add up to the single cross section ofthe larger valve, but with the down side of additional vesselpenetrations and may require a synchronization scheme.

There is a large burst of steam pressure during the rapid opening of thevalve 242, followed by further steam flow for another 30 to 45 secondsas water from the wet biomass evaporates and leaves the reactor. Thismay cool the reactor and the inner screen, which cools to about theatmospheric boiling point of 100 degrees Celsius (212 degreesFahrenheit). This allows subsequent loading of the next biomass batch tooccur without large steam loss and difficulties associated with a hotsurface and wet biomass. A considerable amount of this heat energy iskept in the system by directing the steam to the input hopper 220.Volatile organic compounds (VOCs) derived from the steam explosion stepmay be routed from the steam explosion vessel through the input hopperand directed to a boiler flame to incinerate the VOCs to eliminateemissions of light volatile organic compounds and simultaneouslygenerate heat for the steam explosion step. The steam from the reactionvessel or steam explosion vessel may be fed into the input hopper 220,where some of it condenses and heats the biomass to 100 to 120 degreesF. (40 to 50 degrees C.).

The steam and the entrained volatile chemicals within the fibers arereleased quickly, breaking open the cell from the inside as the interiorpressure is released in response to the release of the exteriorpressure. Physical effects such as de-crystallization of cellulose andhemicellulose occurs in parallel with the breaking of the cell wall. Theresulting biomass particles exhibit an increase in the size and numberof micropores in their fibers, and resultantly, an increased surfacearea. The enhanced surface area and disrupted cellulose (polymer ofglucose sugar monomers) of the biomass exposes the entrained/entrappedsalts to subsequent washing (as detailed below).

Turning back to the overall process detailed in FIG. 2 , the biomassfrom the reaction vessel 240 may pass to a second wash unit 280, whilethe steam (which contains fine particles of beneficiated biomass areentrained therein) passes to a cyclone-type gas expansion vessel (GEV)260 to control the outrush of steam and capture the entrained biomass.The GEV 260 is a large-volume cyclone in which the outrushing steam isintroduced tangentially. FIG. 6 shows a perspective view of the GEV 260,FIG. 7 shows a side view, and FIG. 8 shows a cross-sectional view takenalong line 8-8 of FIG. 7 . A downcomer pipe, or down tube 261, mayextend from the top of the GEV 260 to a position below which the fines,and condensed steam from the reaction vessel is introduced. Somevolatile organic compounds (VOCs) produced in the reaction vessel 240may also be entrained in the out-rushing steam. The down tube 261 mayrelease steam and VOCs from the GEV 260. The steam may be directed fromthe downcomer pipe 261 to the input hopper 220 to conserve BTUs andconvey some moisture and heat to the input biomass. The input hopper 220is not sealed, so pressure does not build up at the input hopper 220.Instead, a fan sucks excess steam pressure and entrained VOCs into thefan and de-mister section 265, wherein the steam is condensed and may beremoved from the gas flow, blowing the VOCs to the air input 252 of theboiler 250 for incineration.

The GEV 260 may serve the purpose of separating the entrained fine,lignin-enriched particulates from the steam and VOCs, and these fineparticulates may drop below the down tube input and be collected. TheGEV 260 may include an input 264 for the steam, VOCs, and fines from thereaction vessel 240, a water input, a gas escape through the downcomerpipe 261 (which may lead to the input hopper 220), and an array ofnozzles 266 for cleaning water and for pre-loading the bottom of the GEV260 with water. The water may be pre-loaded before the explosion stepand thus pre-positioned in the bottom of GEV to catch fines. Also shownare arrows 267 indicating the cyclone in the GEV. A slurry of fines andwater 268 may collect at the bottom of GEV 260, and the slurry of finesand water 268 can exit the base of the GEV 260 through valve/exit 262.

As the steam enters the GEV through input 264, the energy of theresulting vortex is scrubbed through expansion and friction. Biomassparticles drop out to the bottom of the GEV where they can be collectedthrough valve 262, and the steam escapes through the downcomer pipe 261to avoid pressure build-up. The fine particles collected at the bottomof the GEV 260 are enriched in lignin particles. Because of thisdifferentiation, these particles are potentially a valuable by-productas material for other processes (fuel, chemical feedstock,plastics/polymers, sticky binder), and may potentially be collected andtransferred to a washing step or collection bin/auxiliary wash tank 270before further use.

The biomass fines may exit via valve 263 to an auxiliary wash tank 270(or just an output hopper for the fines without a wash step) for removalof fines for separate process due to economic value of the predominantlylignin fine particles. In some configurations, these enriched ligninparticles may be re-blended back to the main product in the second washchamber 280. In other configurations, the enriched lignin particles maybe introduced after the drying process and before pelletization. Inother configurations, the biomass fines may exit via valve 262 at thebottom of the GEV and subsequently be added to the second wash unit 280.In some configurations, the process may be designed to either re-blendthe biomass fines into the product stream (via valve 262) or remove thefines to a separate product stream (via valve 263). In someconfigurations, the process may be design with both valves to allow forboth options. In other configurations, only one valve/exit port 262, 263may be present in same system.

The biomass output from the reaction vessel 240 and potentially thebottom of the GEV 260 may be fed into a separate wash chamber 280. Thiswash chamber 280 may comprise, for example, an agitated/stirred vat or adynamic trommel system, wherein water is contacted with the biomassbeing conveyed via an auger up to drying section (290, 300, 310 in FIG.2 ). While the biomass could be washed within the reaction vessel 240, aseparate tank such as wash chamber 280 may provide better washing andbetter throughput for the reaction vessel, with a better energy balanceand without time wasted in reaction vessel 240 for a wash. It may alsomake the reaction vessel 240 easier and less expensive to manufacture.With the fibers of the biomass disrupted from the chemical and physicalheat and pressure treatment in the reaction vessel 240, salts previouslycaptured between the fibers and within the plant cells are now exposedto being dissolved by the water wash. By dissolving this recalcitrantsalt, the salt can be subsequently removed by extruding the salt-ladenwater in the drying steps 290, 300 (see FIG. 2 ).

Furthermore, small organic materials are produced in the reaction vessel240. These materials have been mostly freed by dissolving a fraction ofthe hemicellulose and side chain moieties broken-off from thehemicellulose, and include sugars, tannins, and small organic acids suchas acetic acid. These materials also get washed out in the wash chamber280, and in the water extrusion processes 290 and 300 along with thesalts. Removing these oxygen-rich organic substances may improve thequality of the fuel because these soluble oxygen-rich organic substancespossess lower heat density than the remaining beneficiated biomass.Removing them therefore reduces the light volatile component of thebiomass, which is problematic in systems like pulverized fuel burnersdue to pre-ignition.

A distinct and separate wash chamber/tank 280 may also allow use of morematerial originally contaminated with salts such as sodium, potassium,and chloride that could have caused slagging, fouling, and corrosion inburners if they had not been washed out. Removal of this extra salt isimportant to economically use some biomass sources such as hogged/slashpiles in the Northwest that have very high salt content. It also allowsuse, for instance, of an entire tree rather than just the heartwoodbecause it can clean the dirt, salt, and light volatiles associatedwith, for instance, leaves from the material. By using entire trees,this process can use less expensive input biomass, including smallinvasive species like Eastern Red Cedar and mesquite that contain noeconomically viable heartwood. Typically, during the process describedherein, sodium, potassium, and chlorine are reduced by 80 to 98 percentof their starting concentrations in the biomass.

In practice, there may be one or more reaction vessel/washingsubsystems. In one configuration, four reaction vessel/washingsubsystems may be provided that share a common GEV and subsequent dryingsubsection. By staggering the filling, reaction, explosion, andunloading times for each reaction vessel/washing subsystem, each of thefour reaction vessel/washing subsystem may be performing a differentstage in the process at any particular moment. In this manner, only oneGEV, drying subsystem, etc., are required, thus simplifying andeconomizing the system as a whole. A more continual heating of severalsmaller reaction vessels or steam explosion vessels rather than theperiodic, more intense heating of one larger vessel may provide a moreefficient use of boiler steam/heat. Loading may be done morecontinuously, steam may be added more continuously (which means lessstress for boiler and hence smaller boiler needed), and unloading may bedone more continuously. Thus, the granularity of a batch process may bereplaced with a more continuous process in terms of loading biomass, useof steam, and unloading biomass product. Sharing common equipment mayalso cut the capital costs of the plant.

As mentioned above, the washed biomass is moved from the post-reactionwash chamber 280 to the dryer sections 290, 300, and 310. The dryersections may be comprised of several processes, and may utilize waterseparation/extrusion steps 290, 300 followed by an evaporative dryer310. Mechanical drying may separate bulk water and dissolved salts andlight volatile organic material from the beneficiated biomass through avibratory screen separator 290 followed by a screw press and/or a rollerpress 300. The vibratory screen separator 290 (e.g., a vibratory screenseparator such as those manufactured by SWECO™) allows water to flowthrough a screen at the bottom of a rotating/vibrating pan. By using twoor more stages (for example, three stacked stages or three successivestages), such as a first screen with holes about 1 millimeter indiameter and subsequent screens with holes about 100 microns and then 39microns in diameter, this “panning” arrangement allows bulk water flowthrough successively smaller holes while keeping the vast majority ofbiomass. The solid captured in each pan is pressed to the outside rimvia a circular motion of the pan, eventually to find an off-ramp whereit is removed and passed to the next step.

FIG. 9 shows a front, perspective view of an exemplary configuration ofa dewatering module comprising of one or more vibratory screenseparators 290 a, 290 b, 290 c, 290 d and an extrusion dryer 300, andFIG. 10 shows a rear, perspective view of the dewatering module of FIG.9 . The dewatering module may generally consist of a vibratoryseparation section 292 (comprising one or more vibratory screenseparators), and a pressing section 302 (comprising one or morepresses). Below the vibratory separation section 292 and the pressingsection 302, a bottom container having one or more storage tanks 294 a-cmay be provided.

Wet biomass may first enter the vibratory separation section 292, and besplit to two vibratory screen separators 290 a, b. These vibratoryscreen separators 290 a, b may have, for example, 1 mm screens. Thus,biomass particles larger than 1 mm (>1 mm particles) may be captured bythe screens and output to the pressing section 302. The water and smallparticles (<1 mm) may drop down to tank 294 a.

The contents of tank 294 a may be pumped up to the next vibratory screenseparator 290 c (in this example, a long SWEECO 290 c as opposed toround SWEECO may be provided, but it will be appreciated that eitherlong or round SWEECOs or other suitable screen separators may be used).The vibratory screen separator 290 c may have a smaller screen, such asa screen of 0.1 mm (100 microns). The particles caught up in the screen(>100 micron particles) may be conveyed to the pressing section 302. Thewater and smaller particles (<100 micron particles) drop down to tank294 b.

The contents of tank 294 b may be pumped up to a final vibratory screenseparator 290 d, which may have an even smaller screen size (forexample, 39 microns). The particles caught up in the screen (forexample, >39 micron particles) may be conveyed to the pressing section302. The water and smallest particles (<39 microns) may drop down totank 294 c, and in some configurations may then be pumped to watertreatment.

The pressing section 302 may include one or more of a simple press, ascrew press, and/or a roller press. The particles caught by thevibratory screen separators may be subject to different types ofpressing depending on their size. For example, the >100 micron and >39micron particles may travel to the simple press, such as rollers 301,where water is squeezed from these small particles (water extruded maypass to tank 294 c). The >1 mm particles may be subject to a screwpress.

The material panned out of the vibratory screen separator(s) 290 may bequite wet, with a moisture content of around 80% and may be transferredto a screw press and/or roller press 300 (FIG. 2 ) for furtherextrusion. The screw press 303 (visible in FIG. 10 ) may comprise anauger, a screen, and an end plug, with the auger pushing the materialagainst the screen and against the end plug which may be held place withair pressure (different pressures may be used depending on the desiredoutcomes; in some configurations, a pressure of about 50 psi may beused). Depending on the run conditions above (original maceration size,whether or not fines from gas expansion vessel have been added back in,retention time in the reaction vessel, etc.), there may be differentsize and softness of washed biomass. Smaller material may squeezethrough screen, necessitating less pressure be applied to the plug.Larger or less soft material might plug the screw press, and maynecessitate slower feed and throughput. The requirements of dryermaterial may also necessitate slowing down the screw press andmaximizing plug pressure. Material squeezes out around the end plug at amoisture content of around 30% to 60% and may then be sent to acontinuous roller press (such as rollers 301 in FIG. 10 ).Alternatively, the material may be passed from the screw press to anevaporative dryer.

The roller press operates at an effective pressure of around at least1000 psi, with around 2000 to 3000 psi being more typical. With thefibers and fiber cells disrupted by the reaction vessel processes andfurther sheared in the screw press, the water is accessible and isessentially “surface” water, amenable to extrusion via roller press.Without the fiber disruption caused by the reaction vessel, 10,000 psiwould not be sufficient to obtain these results.

The roller(s) 301 of the roller press can be embossed with either adiamond or herringbone design, mainly to trap the biomass material andcarry it under the rollers. The roller(s) 301 may have a permeable beltunderneath, and a vacuum applied to the permeable belt under the rollermay aid in sucking the water away. The shear forces exerted by theextrusion dryer(s) 300 (screw press and/or roller press) may pulverizedthe particles down to an average size of hundreds of microns. Materialleaving the roller press may have moisture of content of around 30% orhigher. After different sized particles are subject to their respectivepresses, they may be re-combined with the other particles. There-combined particles are conveyed to the evaporative dryer section 310via a conveyor 305.

After the extrusion dryer(s), material may be transported to anevaporative heater 310 to get the moisture content down to between about7% to about 13%, which is considered a good moisture content for makingpellets. The evaporative heater 310 may be constructed in several typesof configurations. For example, a simple configuration of theevaporative heater simply runs the material along a conveyor beltthrough a hot room with air stream or ventilation, where the heat may beat least partially supplied from the contained exhaust of the boiler 250via a connection 253 between the exhaust of the boiler and theevaporative heater 310 (FIG. 2 shows schematically the connection 253between the boiler 250 and the evaporative heater 310). In someconfigurations, a moisture sensor may be included, with a feedbackmechanism to automatically adjust the parameters for a consistent finalmoisture content. FIG. 11 shows a perspective view of an evaporativeheater 310, with an inlet 315 for biomass from the extrusion dryers.

A more forceful configuration may suck the material through a flashdryer, consisting of a serpentine set of pipes leading to a vortex, tocapture dried particles. The biomass may be sucked into a stream of hotair (for example, around 300° to 420° F.) through a rotating air-lockvalve, causing it to fly and crash into the barriers repeatedly, thusbreaking up the biomass into micron-sized particles. Pipes along thestraight lengths may have a larger diameter than pipes along the cornersto maximize the crashes of the particles into side barriers and increaseresidence time. The material is removed via a second air lock andallowed to cool. Another possible configuration of an evaporative heater310 may be a commercially available evaporative dryer such as afluidized bed dryer. Ideally the oxygen content of this air should bekept below about 14% to prevent any combustion. Nitrogen is anotheralternative, or the sub-saturated steam from the evaporating water fromthe biomass supplemented with a small amount of steam from the boilermay be used to inert the atmosphere.

Whatever configuration is used, the evaporative heating stage furtherremoves remaining light volatile chemicals and lightly pyrolizes thebiomass, increasing the friability and therefore improving grindability.The friability imparted by both the steam explosion in the reactionvessel 240 and the drying process 310 is a unique characteristic for thebiomass material produced as a result of the process described herein:the fibers which make up biomass typically impart a stringiness to thematerial when produced from other processes that prevent grinding to asize distribution typical of coal. The dried biomass at this point istypically a brown powder ready to be pelletized or briquetted fortransportation. It may be stored in a product hopper 325 (FIG. 11 ).

Energy may be conserved and used throughout the process describedherein, particularly the steam produced in the reaction vessel 240. Forexample, referring to the overall process in FIG. 2 , steam/biomassfines/VOCs leave the reaction vessel 240 in steam explosion throughrapid release valve 242 and go to the GEV 260. In the GEV 260, thebiomass fines lose energy in the cyclone and drop to the bottom. Thesteam and VOCs escape (due to pressurization) through the downcomer pipe261, which may be connected to the input hopper 220 through connection221. The head space of the input hopper 220 may be large enough toaccommodate this on-rush of pressure (with the headspace approximatelyequal to volume of biomass stored in hopper), and a pressure reliefplate may be installed to keep the pressure below 5 psig (a thin-walled55 gallon drum may withstand a pressure of 6 psig).

In the input hopper 220, the steam gives up most of its heat energy,condensing to hot water in contact with the input biomass, thus startingthe chemical processes involved in beneficiation. As some of the steamcondenses, it may heat the biomass to 100 to 120 degrees F. (40 to 50degrees C.) to start the chemical processes.

Any remaining pressure from the steam explosion step is vented throughpipe 222 or output 222 in input hopper 220, which may be connected tothe boiler 250. In addition to this periodic pressure increases due tosteam explosion, a fan may also be provided to drive the process bypulling air through fan/demister pad unit 265. The demister pad mayremove the remaining steam/condensate and allow the VOCs to proceed tobe mixed into the air intake of the boiler 250 and hence to be burned inthe boiler rather than exhausted to the atmosphere. Thus, VOCs derivedfrom the steam explosion step may be routed from the steam explosionvessel through the input hopper and directed to a boiler flame toincinerate the VOCs to eliminate emissions of light volatile organiccompounds and simultaneously generate heat for the steam explosion step.

It will be appreciated that fabrication of the system may beaccomplished many different ways. To facilitate assembly and maintainthe possibility of moving the system to different sites without completedisassembly and re-assembly, components may be built to fit intostandard transportation containers. This may also allow easy equipmentmovement. The containers may also provide inexpensive support structurefor some of these components. Finally, the use of Victaulic-typecouplings for non-pressurized pipe runs may have some advantages,including ease of assembly for containerized parts, cleaning out anyclogs, and ease of maintenance.

EXAMPLES

The process employed a chipper to appropriately size and expose surfacearea. Generally, materials were macerated to about 1.27 to 0.635centimeters (one-half to one-quarter inch) and smaller size, but largerpieces of biomass were used. As noted in Table 1, there was a tradeoffin chipping to smaller sizes versus the pressures/retention timesrequired in the reactor. For example, 1.27 centimeter-sized(one-half-inch) Empty Fruit Bunch (EFB) could be beneficiated at 350 psisaturated steam and half hour retention time, while 5.08centimeter-sized (2 inch) EFB required 385 psi saturated steam and 25minutes retention time. Various reaction conditions are possible, and itwill be appreciated that numerous combinations of reaction conditionsare contemplated. Table I shows the chip size, solvent, temperature,etc., used for each type of biomass in one example. Table II shows thechip size, solvent, temperature, etc., used for each type of biomass inanother example.

TABLE I TRUNKS EMPTY FROM FRUIT MALAYSIAN MIXED PALLETS BUNCHES PALMDOUGLAS HOGGED WOOD (KILN (EFB) TREES FIR FUEL IDAHO DRIED) Chip size 2½ to 1 1 to 2 ¼ to 1 ⅛ to 1/4 sawdust (inches) Solvent used water waterwater water water water in pre-wash Temperature 190 to 195 200 to 202200 to 202 200 to 202 200 to 202 201 to 204 of the reaction vessel(degrees C) Pressure of 195 to 200 210 to 220 210 to 220 210 to 220 210to 220 215 to 230 the reaction vessel (psig) Residence 20 to 25 25  30   30   30   35 to 40 Time in reaction vessel (min) Starting 8.8 67.855.6 30.4 27.5 3.7 water content (%) Final water 8.5  7.1  4.7 No data 9.3 4.7 content (%) % fixed 13.6 → 18.1 14.0 → 17.6 10.6 → 20.2 24.0 →33.8 13.7 → 20.8 12.5 → 13.3 carbon (dry basis) (start→finish) %volatiles 81.8 → 79.2 79.2 → 79.6 87.8 → 78.1 81.6 → 65.7 85.4 → 78.586.3 → 76.3 (d/b, both light and heavy volatiles) (start→finish) % ash(d/b) 2.84 → 2.96 6.26 → 2.60 0.10 → 0.10 0.92 → 0.73 0.75 → 0.38 0.63 →0.56 (start→finish) Heat content 7939 → 9346 7758 → 8981 8443 → 9805  8923 → No data 8699 → 9888 8796 → 9500 (BTU/pound) (start→finish) Salt8720 → 344  24800 → 457  328 → <85    811 → No data N/D N/D reduction K⁺(ppm) (start→finish) Salt  131 → <100  515 → <100 <95 → <85    115 → NoData  612 → <100 N/D Reduction Na⁺ (ppm) (start→finish) Salt  0.12 →<0.10 1.22 → 0.13 <0.10 → <0.10 N/D  0.11 → <0.10 N/D reduction Cl⁻ (wt%) (start→finish)

TABLE II Trunks Empty from Fruit Malaysian Mixed Pallets Bunches PalmDouglas Hogged Wood (kiln (EFB) Trees Fir Fuel Idaho dried) Chip size 2½ to 1 1 to 2 ¼ to 1 ⅛ to ¼ sawdust (inches) Solvent used water waterwater water water water in pre-wash Pressure of 385 to 400 400 to 420410 to 420 410 to 420 410 to 420 415 to 430 reaction vessel (psig)Temperature 227 to 229 229 to 232 231 to 232 231 to 232 231 to 232 231to 233 of reaction vessel (degrees C) Residence 20 to 25 25   30   3030   35 to 40 Time in reaction vessel (min) Starting 8.8 67.8 55.6  30.4 27.5 3.7 water content (%) Final water 8.5  7.1  4.8 10  9.3 4.7content (%) % fixed 13.6 → 18.1 14.0 → 17.6 10.6 → 20.2 24.0 → 33.8 13.7→ 20.8 12.5 → 13.3 carbon (dry basis) (start→finish) % volatiles 81.8 →79.2 79.2 → 79.6 87.8 → 78.1 81.6 → 65.7 85.4 → 78.5 86.3 → 76.3 (d/b,both light and heavy volatiles) (start→finish) % ash (d/b) 2.84 → 2.966.26 → 2.60  0.10 → >0.10 0.92 → 0.57 0.75 → 0.38 0.63 → 0.56(start→finish) Heat content 7939 → 9346 7758 → 8981 8443 → 9805  8923 →10,617 8699 → 9888 8796 → 9500 (BTU/pound) (start→finish) Salt 8720 →344  24800 → 457  328 → <85 811 → 354 N/D N/D reduction K⁺ (ppm)(start→finish) Salt  131 → <100  515 → <100  95 → <85  115 → <100  612 →<100 N/D Reduction Na⁺ (ppm) (start→finish) Salt  0.12 → <0.10 1.22 →0.13 <0.10 → <0.10  0.006 → <0.006  0.11 → <0.10 N/D reduction Cl⁻ (wt%) (start→finish)Pre-Wash Unit

The chipped biomass input is introduced to a pre-wash processing unit.For studies in Table I, the chips are placed into a stainless steelcylindrical cage, with a diameter of about 20 centimeters (about 8inches), a length of about 3.13 meters (about 10 feet, 4 inches), atotal volume of about 102 liters (6230 cubic inches), with 0.47centimeters ( 3/16 inch) holes in the cage. The chips are placed in thestainless steel cylindrical cage, and both ends are closed. The loadedbasket is washed with a hose and then dunked in a trough filled withwater, where it is agitated for a minute and allowed to sit for about 10to 15 minutes before being removed and allowed to drip for 3 to 5minutes. Alternatively for Douglas Fir and Oregon Hogged Fuel, the chipsare loaded into a trammel semi-submerged in water (trammel detailsabove). The material is augered through the water in the trammel, whereit empties to a conveyor belt and then dropped into the basket describedabove.

Reaction Vessel or Steam Explosion Vessel

The basket or cage, still dripping wet from the previous wash step, isslid into the reactor through an open o-port, which is then closed.Steam from a boiler is applied to the 290 psi limit the boiler cansupply. From there, the temperature and pressure are increased byheating the reaction vessel or steam explosion vessel 240 with electricband-heaters surrounding the stainless steel reactor to reach thedesired pressure of around 400 psi. If necessary, further reaction timeis allowed at the final desired pressure. The reaction vessel'stemperature, pressure, and biomass residence time are carefullycontrolled so as to optimize process conditions for a particular biomassinput as set forth in Table I.

After a desired reaction time, the rapid release valve is opened in <0.5seconds. In the studies for Table I, this valve consisted of a 3″diameter pneumatically actuated ball valve pressurized to 130 to 150psi. The resulting rapid pressure release produced a stream ofoutrushing steam that is piped to the gas expansion vessel. Theperforated screen, which had allowed a better ingress of the steam tothe biomass, now gives a larger cross section for rapid release andegress.

Gas Expansion Vessel

In addition to the beneficiated material left in the basket, fineparticles of beneficiated biomass are entrained in the stream ofreleased steam. A gas expansion vessel is used to control the outrushand capture the entrained biomass. The gas expansion vessel is alarge-volume cyclone in which the outrushing steam is introducedtangentially. A downcomer pipe is built into the center top of the gasexpansion vessel to give the steam eventual egress so the pressureinside the gas expansion vessel remains low. As the energy of theresulting vortex is scrubbed through expansion and friction, biomassparticles drop out to the bottom of the gas expansion vessel where theyare collected, and the steam escapes through the downcomer pipe to avoidpressure build-up. The fine particles are collected and transferred tothe second wash unit where they are recombined with the contents of thebasket.

Second Wash Unit

The biomass output from the reaction vessel and the bottom of the gasexpansion vessel are fed into a separate, second wash chamber. This washchamber comprises a vat agitated/stirred by compressed air, whereinclean water is contacted with the biomass. With the fibers of thebiomass disrupted from the chemical and physical heat and pressuretreatment in the reaction vessel, salts previously captured between thefibers and within the plant cells are exposed and dissolved by the waterwash. By dissolving these recalcitrant salts, the salts (especiallyconsisting of sodium, potassium, and chloride ions which causecorrosion, slagging and fouling) are subsequently removed by extrudingthe salt-laden water in the drying steps. Furthermore, small organicmaterials are produced in the reactor. These light volatile materialsalso get washed out in the wash chamber/water extrusion processes alongwith the salts.

To determine the amount of light volatile material removed, the weightof material lost upon heating from 105 degrees C. to 250 degrees C. ismeasured, for the raw biomass and for the beneficiated biomass. Thematerial is first heated to 105° C. to drive off the moisture in thematerial. The dried weight is noted after the material reaches a steadyweight (typically 45 minutes to 1 hour). The material is then heated to225° C. for several minutes, followed by 5° incremental temperatureincreases to 250° C. After an hour, the weight stabilizes and is noted.The weight loss represents the amount of light volatile material thatcould be problematic in subsequent use as a fuel. As noted in Table I,on a dry basis, herbaceous material went from a range of 40 to 70% downto a range of 30 to 40%, soft woods went from a range of 60 to 80% downto a range of 30 to 50%, and hard woods went from a range of 40 to 50%down to a range of 35 to 45%. By reducing the amount of light volatiles,the material is made more coal-like.

Dryer Sections

The washed biomass slurry is pumped from the post-reaction wash sectionto the dryer sections. The dryer sections are comprised of severalprocesses, using water separation/extrusion steps followed by anevaporative final dryer. Bulk water is separated from the beneficiatedbiomass through a vibratory screen separator (SWECO Vibro-EnergySeparator) or filter sock (50 micron filter) followed by a screw press(Vincent Screw Press). The vibratory screen separator allowed free waterto flow through a screen at the bottom of stacked rotating/vibratingpans. Three stacks are used with screen sizes of 1 mm, 100 micron, and39 micron screens. This panning arrangement allows bulk water seepthrough while keeping the vast majority of biomass on top of the threescreens. The resulting water is only faintly colored—any furtherscreening for smaller particles may not be cost effective. The solidcaptured in each pan is pressed to the outside rim via a circular motionof the pan, eventually to find an off-ramp where it is removed andpassed to the next step.

The use of three stacked pans to capture the material rather than justone pan using the 39 micron screen may decrease clogging the screen. Byspreading the material by size through three screens rather than onlyone with the very smallest hole size, the potential to clog reduces,thereby letting the water to drip through the screens rather thanponding on the surface of a clog.

The material panned out of the vibratory screen separator or removedfrom the filter sock is wet, with moisture contents different fordifferent sized particle layers. A moisture content of 80 to 85% remainsin the 39 to 100 micron fraction, while the larger-sized fractionsretain 70 to 80% moisture content.

The combined material is transferred to a screen compression press forfurther water extrusion. An auger pushes the material against a screenand against an end plug held in place with about 50 psi pressure.Material squeezed out around the end plug at a moisture content of about45 to about 60%. The shear forces exerted by the screw press pulverizethe particles down to an average size of hundreds of microns.

Finally, the material is transported to an evaporative heater to obtaina moisture content of 10±3%, the preferred moisture content for makingpellets. Some of the samples (Douglas Fir, Hog Fuel) are put through adryer (Stelter and Brink, LTD SSP Dryer), which runs the material alonga conveyor belt or vibrating ramp through a hot room with hot airstream. Under a moderate air flow, the dried material is blown off thebulk material and into a cyclone collector. The final moisture contentof the beneficiated biomass can be roughly controlled by the dryerconditions such as the burner temperature (410° F. to 435° F.) and fanspeed.

Table III shows the results for six different drying tests, performedusing Douglas Fir and Oregon Hog Fuel. Each test started off with amoisture content of 40%. The burner temperature, plenum temperature, andfinal moisture content were measured.

As seen in Table III, there is some variation in the resulting finalmoisture content between similar tests (for example, test 4 vs. test 5in Table III).

TABLE III BURNER PLENUM FINAL TEMPER- TEMPER- FAN MOISTURE ATURE ATURESPEED CONTENT (%) TEST (F.) (F.) (HZ) (START→FINISH) 1 390 310 50.540→20 2 413 328 50.5 40→18 3 435 355 42.8 40→7  4 430 345 42.8 40→8  5431 345 42.8 40→12 6 435 346 42.8 40→6 

Other samples (EFB, Malaysian trunks, pallet material) are put through aflash dryer, consisting of a serpentine set of pipes leading to avortex, to capture dried particles. The biomass is sucked into a streamof hot air (390° F. to 420° F.) through a rotating air-lock valve andcaused to fly and crash into the barriers repeatedly, thus breaking upthe biomass into micron sized particles. The material is separated fromthe created steam in a cyclone stage and removed from the cyclone andallowed to cool. Several cycles may be required to get the moisturecontent down to around 10%.

In various configurations, this evaporative drying stage further removeslight volatile chemicals and lightly pyrolizes the biomass, causing itto be more friable and therefore have better grindability. The driedbiomass at this point is a brown powder ready to be pelletized orbriquetted for transportation. It may be stored in a product hopper.

Friability is an important factor when considering a fuel for mixingwith or supplanting coal in a utility pulverized coal power plant, wherethe pellets would be put through a bowl mill for pulverization the sameway that coal is. Milling tests using the dried biomass preparedaccording to the present disclosure were conducted. A one ton/hourmilling test was conducted using a 15%:85% (dried biomass:Sufco coal) byweight mixture. Dried biomass included beetle kill Ponderosa,Douglas-fir, Spruce, and Pinyon from Manti-La Sal Forest. Conclusionsreached for the 15/85 mixture versus 100% coal include: high heatingvalue of mixture 10,246 BTU/lb vs 10,551 BTU/lb for 100% coal; millpower requirements were not increased; no increase in the fraction oflarge particles of milled material; requirement of 70% pass-through 200mesh was achieved (i.e., 70% of particles in the powder are less than 74microns in size, and pass through a screen with 200 mesh (200 wires perinch, hole size of 74 microns)); mill outlet temperature was onlyslightly higher for blend, indicating no unwanted reaction in mill.

Thus there is disclosed multiple configurations, systems, and methodsfor beneficiating and cleaning biomass. It will be appreciated thatnumerous modifications may be made without departing from the scope andspirit of this disclosure. The appended claims are intended to coversuch modifications.

What is claimed is:
 1. An apparatus for pretreating a biomass, theapparatus comprising: a reaction vessel for pressurizing and rapidlydepressurizing a biomass within the reaction vessel, wherein thereaction vessel comprises an inner perforated screen forming a cage forholding the biomass and separating the biomass from a wall of thereaction vessel, and wherein the inner perforated screen forming a cagefurther comprises one or more perforated screen fingers positionedwithin the biomass during pressurization of the biomass to increaseexposure of the biomass to steam.
 2. The apparatus of claim 1, whereinthe one or more perforated screen fingers are positioned away from awall defining the reaction vessel.
 3. The apparatus of claim 1, furthercomprising a separate wash chamber, the separate wash chamber beingapart from the reaction vessel.
 4. The apparatus of claim 3, wherein theseparate wash chamber is able to remove at least 5 percent of saltsderived from a disrupted biomass.
 5. The apparatus of claim 3, whereinthe separate wash chamber is able to remove at least 10 percent of thesalts and light volatile organic compounds derived from a disruptedbiomass.
 6. The apparatus of claim 3, wherein the separate wash chambercomprises a dynamic trommel.
 7. The apparatus of claim 3, furthercomprising a screw press for mechanical drying.
 8. The apparatus ofclaim 3, further comprising a continuous roller press to remove water.9. A system for pretreating a biomass before forming a pellet, thesystem comprising: a reaction vessel for pressurizing and rapidlydepressurizing a biomass within the reaction vessel, the reaction vesselcomprising an inner perforated screen forming a cage, the cage forholding the biomass and for separating the biomass from the main body ofthe reaction vessel, the cage further comprising one or more perforatedscreen fingers positioned within the biomass held in the cage toincrease exposure of the biomass held in the cage to steam; and aseparate washing container configured to remove at least one of saltsand light volatile organic compounds derived from the biomass.
 10. Thesystem of claim 9, further comprising a mechanical continuous waterremoval mechanism configured to remove water from the biomass to producea biomass having less than about 50% water by weight; and an evaporativeheating chamber configured to evaporatively remove an additional portionof the water from the biomass and produce a friable biomass, wherein thefriable biomass comprises less than about 25% water by weight.
 11. Thesystem of claim 10, further comprising a routing and fan-driven systemfor routing remaining volatile organic compounds to an air input of aboiler for incineration.
 12. A steam explosion system for treating abiomass, the steam explosion system comprising: a reaction vessel forpressurizing and rapidly depressurizing a biomass within the reactionvessel, wherein the reaction vessel comprises an inner perforated screenforming a cage for holding the biomass, the cage being suspended withinthe reaction vessel to separate the biomass within the cage from a wallof the reaction vessel, and wherein the cage further comprises oneperforated screen finger positioned at a center of the cage to increaseexposure of the biomass to steam.